Exposing nanobubble-like objects to a degassed environment

Abstract

The primary attribute of interest of surface nanobubbles is their unusual stability and a number of theories trying to explain this have been put forward. Interestingly, the dissolution of nanobubbles is a topic that did not receive a lot of attention yet. In this work we applied two different experimental procedures which should cause gaseous nanobubbles to completely dissolve. In our experiments we nucleated nanobubble-like objects by putting a drop of water on HOPG using a plastic syringe and disposable needle. In method A, the nanobubble-like objects were exposed to a flow of degassed water (1.17 mg/l) for 96 hours. In method B, the ambient pressure was lowered in order to degas the liquid and the nanobubble-like objects. Interestingly, the nanobubblelike objects remained stable after exposure to both methods. After thorough investigation of the procedures and materials used during our experiments, we found that the nanobubble-like object were induced by the use of disposable needles in which PDMS contaminated the water. It is very important for the nanobubble community to be aware of the fact that, although features look and behave like nanobubbles, in some cases they might in fact be or induced by contamination. The presence of contamination could also resolve some inconsistencies found in the nanobubble literature.

Surface Nanobubbles Studied by Time-Resolved Fluorescence Microscopy Methods Combined with AFM: The Impact of Surface Treatment on Nanobubble Nucleation

“…By contrast, after exchanging the ethanol again with water, the surface was found to be covered with round structures that correspond to previous work reporting on surface nanobubbles (Figure 1c). Even though no disposable syringes or needles, which are known to introduce polysiloxane based 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 contamination into the liquid cell and onto the sample surface, 21,43 However, unlike following this indirect degassing strategy, which cannot differentiate easily a volatile water-insoluble organic liquid from gas, the work discussed here exploits FLIM, which identifies the gas-filled surface nanobubbles via the characteristic emission component lifetime of the reporter dye Rh6G, when it is partitioned to the gas-water interface. We have verified in independent measurements that water surface tension demonstrates some decrease in the presence of Rh6G.…”

Phase State of Interfacial Nanobubbles

“…20 How can one directly distinguish between oil droplets and air bubbles in situ? Optical microscopy is very versatile and allows visualization of many dyes that would absorb into oils.…”

Evidence of slippage breakdown for a superhydrophobic microchannel

“…The authors explained such a behaviour by assuming the presence of some surface-active impurity, which contaminated the liquid-air interface. A recent experimental study on nanobubble-like object generation 38 reported the unexpected presence of PDMS contaminant in sterile disposable needles, which made clear how difficult is to control the presence of impurity within a sample even when working with standard microfluidic cleaning procedures.…”